Nitrogen oxides (NOx), which are exhaust gases produced from a power station using, as a main fuel, coal, heavy oil and gas, is the main culprit of air pollution and much cost is required for treating the NOx gas.
When nitrogen oxides are decomposed with a catalyst for high efficiency selective catalytic reduction (SCR), which is one of catalysts for the removal of nitrogen oxides, air pollution can be efficiently reduced with a low cost.
The catalyst for selective catalytic reduction (SCR catalyst) mainly comprises a support such as titania, alumina, silica and zirconia, and oxides of active metals such as vanadium, molybdenum, nickel, tungsten, iron and copper. In particular, the commercial selective catalytic reduction techniques mostly deal with V2O5/TiO2 catalysts. Further, various SCR catalysts for the removal of nitrogen oxides from exhaust gases are known in several patent documents including Korean Patent Nos. 382051, 473080 and 275301.
The process of selective catalytic reduction (SCR) has been used for a long time in the power station sector to remove the nitrogen oxides from exhaust gases. Herein, ammonia (NH3) is introduced into exhaust gases and is selectively reacted with the nitrogen oxides on a suitable catalyst to obtain nitrogen and water.
In the past, a method for manufacturing the most generally known catalytic module element in connection with selective catalytic reduction (SCR) techniques includes wash coating and extrusion.
The wash coating is a technique that is used in manufacturing a catalytic converter used as an automobile exhaust emission control system and in which a catalyst is thinly coated on the surface of a cordierite in the form of honeycomb (grid-type square brick form). However, this process is difficult to mass-produce a catalyst since the whole operation is manually performed in the selective catalytic reduction for many stationary sources and is not economical in that expensive cordierite is used as the support and hence the competitive price is lower than a process directly extruding an inexpensive catalyst.
Meanwhile, the extrusion generally uses a honeycomb produced through an extrusion manner by converting SCR powders into a highly viscous liquid phase. However, the honeycomb produced through the extrusion manner has problems in that is heavy and there are cracks in a molded article during drying and baking of the molded and extruded product, it is not economic because longer times are required in baking, and physical strength is lowered. In other words, cracks are generated because an exothermic reaction occurs in a drying step of a catalyst and thus an organic binder is suddenly volatilized. Further, the extrusion has problems in that the removal efficiency of nitrogen oxides is low and various types of catalytic module elements cannot be manufactured.